At present, a high molecular weight phenylene ether compound, for example a polyphenylene ether resin (to be referred to as “PPE” hereinafter, for instance JP-B-S42-3195 and JP-B-S58-53012), is applied to electric and electronic material uses and constructional material uses since it shows excellent high frequency properties, heat resistance and flame resistance. That is, in addition to its excellent properties, PPE also has a phenolic hydroxyl group which is easily modifiable with a functional group in accordance with an intended use. However, the range of its usage is limited because PPE is poor in compatibility with a thermosetting resin such as an epoxy resin or a cyanate resin, which is used in the fields of electric and electronic materials, also poor in solubility in general-purpose solvents, and furthermore poor in compatibility with other plastics which are used for constructional materials. Therefore, the excellent properties of PPE are not exploited in a variety of fields. Accordingly, for example, a method of IPN (interpenetrating polymer network) structuralization with a cyanate resin (for example Japanese Patent No. 3261076), a method of converting a high-molecular weight PPE into a low-molecular weight PPE by means of a radical catalyst (for example Japanese Patent No. 3248424) and a method of oxidatively polymerizing a bivalent phenol compound and a monovalent phenol compound (for example JP-B-H8-011747) have been proposed for the purpose of expanding the usage range of PPE. Furthermore, a method of producing a phenylene ether oligomer by oxidative polymerization of a specific bisphenol compound and a specific monovalent phenol compound (for example JP-A-2003-12796) has been also studied. However, it is difficult to precipitate, as particles, a phenylene ether oligomer obtained by the above method. This is a problem in view of industrial manufacturing.
That is, generally, a polyphenylene ether resin is obtained in an aromatic hydrocarbon solution and alcohols such as methanol are used for forming particles thereof. When the same method is applied to a phenylene ether oligomer, a low molecular weight substance dissolves in an alcohol such as methanol so that it is impossible to obtain particles efficiently. Further, when water is added in order to decrease the solubility in an alcohol, precipitation of a viscous substance appears. Therefore, this method is also industrially inappropriate.
It is an object of the present invention to provide an industrial process for the production of a phenylene ether oligomer which utilizes the excellent electrical characteristics, heat resistance and flame resistance of a phenylene ether structure, has remarkably high compatibility with other resins and remarkably high solubility in general-purpose solvents and also has a phenolic hydroxyl group easily modifiable in accordance with an intended use, which process is capable of easily precipitating the phenylene ether oligomer as particles.